This study was to examine the impacts of staff-child ratio on the quality of care and education for toddler-age children through controlling the variables of demographic features and structural characteristics of the compared classrooms. Two toddler classrooms in Hong Kong adopting different staff-child ratios were selected for the comprehensive quality assessments by using the Infant/Toddler Environment Rating Scale - Revised (ITERS-R) approach. The findings indicated a negative association between the staff-child ratio and the global quality of centre-based care and education for toddlers. The quality related to the "Interaction" and "Personal Care Routines" was found to be significantly related to the ratio, while the quality associated with the "Space and Furnishings" and "Program Structure" was less affected. The results of the study demonstrate the applicability of the ITERS-R in a new cultural and linguistic environment, and provide information on how staff-child ratio affects various aspects of the quality of care and education for toddlers. Copyright © 2019 The Author(s). All Rights Reserved.